Bacterial Morphology and physiology Flashcards
what is the difference between bacterial cells and mammalian cells?
bacterial cells = prokaryotes = no nucleus, cell wall, no cell organelles
eukaryotes = nucleus, no cell well, and contain cell organelles
what are the features of a gram positive organism
gram - pos = have a thick layer of peptidoglycan surrounding the cell membrane and have low cell - wall lipid content
what properties does a gram negative organism have?
they have a thin peptidoglycan layer and high cell-wall lipid content
what reagents are used in a gram staining process?
1) crystal violet
2) iodine (fixes violet color)
3) alocohol - takes out violet color in gram negative organisms
4) neutral red - dyes the gram negative bacteria, and does not effect the gram positive
why does alcohol have it’s effect on gram positive/negative organisms?
gram positive = have low lipid content and is therefore dehydrated by alcohol making it impermeable
gram negative = high lipid content which is extracted by alcohol to permeabilise the membrane= red color
what sort of organism do we use a Ziehl-Neelson stain for?
mycobacteria
they are not stained using gram stain due to a high wax content in cell envelope
You should know these
Describe the bacterial cell structure
genome
cytoplasmic membrane
cell wall
outer membrane of gram - negative bacteria
capsules/slime layers
What does cytoplasm contain?
composed of approx 80% water
contains enzymes that breakdown glucose and other carbon sources to provide energy - enxymes involved in cell wall synthesis
ribosomes - protein synthesis
genome - single tightly folded molecule of double stranded DNA - chromosomal DNA and also small circular extrachromasomal DNA - plasmid DNA
what is the role of the cytoplasmic membrane?
composed primarily of lipids and proteins -
hyrdrophilic portion of lipid faces towards the aqueous environment
- acts as osmotic barrier -
- transports-
- site of energy production (electron transport chain)
what is peptidoglycan?
primary component of the bacterial cell wall
prevents osmotic lysis
gram negative bacteria have one or two peptidoglycan layers
gram positive bacteria have many peptidoglycan layers
what lies on the surface of gram-positive organisms?
they have wall teichoic acid and lipoteichoic acid strains on the surface
what does the gram negative bacterial cell wall/envelope consist of
gram negative cells have cell membrane, then thin layer of peptidoglycan, then outer cell membrane
-
what is the function of the gram-negative cell envelope?
bacterial cell adhesion
resistance to phagocytosis
molecular sieve
LPS - has important role in inflammation and infections - triggers an immune response which may be protective or pathogenic if uncontrolled
what is the function of pili?
common pili = they adhere to things
conjugative pili = plasmid transfer- allow transfer of genetic information
what is the function of spores?
gram- poistive bacteria can form spores which provide protection from adverse conditions
they are dormant cells but when introduced into a wound site they can germinate and cause infection
*ex. C. Dif
can gram-negative bacteria form spores?
no
Why are spores dangerous?
they can germinate and transmit disease
they are resistant to heat, drying, radiation, freezing, toxic chemicals, antibiotics,
must have proper autoclaving to kill a spore
what is the purpose of a capsule/slime layer?
capsules = tightly associated
slime = loosely associated
both are polysaccharide or protein layers that surroudn many baterial cells
they provide protection from phagocytosis and antibiotics and play a role in bacterial adherence
what is the role of biofilms?
they form when bacteria adhere to surfaces and excrete slimy glue-like substances which anchor the cells and allow them to form a community
why do biofilm infections persist?
because the cells in a biofilm are protected from the immune response
antibiotics cannot penetrate biofilm well and therefore cannot reach cells
enzymes in teh biofilm matrix may destroy antibiotics
biofilm cells have altered metabolism slowly dividing cells may not be as susceptable to antibiotics
describe the phases of growth in a bacterial culture
1) lag phase = adaptation
2) logarithmic phase = cells multiply at the maximum rate
3) stationary phase = lack of nutrients and buildup of toxic metabolic intermediates means multiplication is balanced by cell death
4) phase of decline
why is the growth phase of a bacteria clinically relevant?
becuase infections may involve bacteria in different stages, some antibiotics work better on rapidly growing cells, but not cells in a plateau
where do clinically relevant bacteria obtain energy?
it is derived from teh enzymatic breakdown of organic substrates ( carbs, lipids, proteins) - in a process called catabolism
energy generated from catabolism is used to synthesise cellular consituents in a process called anabolism
in obligate anaerobes, what is the final electron acceptor in anaerobic respiration?
They cannot use oxygen as the terminal acceptor because the superoxides generated would be toxic if not detoxified by the superoxide dismutase which they lack.
